The User-Agent header recently become required to fetch blacklist from URL

  https://ahmia.fi/blacklist/

[1] https://github.com/searxng/searxng/actions/runs/18892940199/job/53924400294

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

This is an old and grumpy hack / SearXNG is a Flask application with
client/server structure, which can't be turned into a command line tool the way
it was done here.

Maintaining this hack is becoming increasingly complex the more we try to
remodel the core code, which is why we should now remove the hack from SearXNG.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

In 25.1.0 [2] an old bug has been fixed: "Docstring formatting does not apply to
module docstrings" [3].

[1] https://github.com/psf/black/blob/main/CHANGES.md#2590
[2] https://github.com/psf/black/blob/main/CHANGES.md#2510
[3] https://github.com/psf/black/issues/4094

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Continuation of #5147 .. typification of the engine processors.

BTW:

- removed obsolete engine property https_support
- fixed & improved currency_convert
- engine instances can now implement a engine.setup method

[#5147] https://github.com/searxng/searxng/pull/5147

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

- pyright configuration [1]_
- stub files: types-lxml [2]_
- addition of various type hints
- enable use of new type system features on older Python versions [3]_
- ``.tool-versions`` - set python to lowest version we support (3.10.18) [4]_:
  Older versions typically lack some typing features found in newer Python
  versions.  Therefore, for local type checking (before commit), it is necessary
  to use the older Python interpreter.

.. [1] https://docs.basedpyright.com/v1.20.0/configuration/config-files/
.. [2] https://pypi.org/project/types-lxml/
.. [3] https://typing-extensions.readthedocs.io/en/latest/#
.. [4] https://mise.jdx.dev/configuration.html#tool-versions

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
Format: reST

Compared to ``lightbulb`` theme we used in the past for the dark theme, the
``monokai`` has a better contrast [1].

BTW, the result list of SearXNG should not act as a code-checker: The border &
color of class ``.err`` (used for syntax errors) has been removed / code
snippets are often not well formed nor valid code and the rendering of such code
fragments as errors obscures the view on the code snippet.

[1] https://pygments.org/styles/

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>